Contemporaneous Broadband Observations of Three High-redshift Bl Lac Objects

We have collected broadband spectral energy distributions (SEDs) of three BL Lac objects, 3FGL J0022.1−1855 (z=0.689), 3FGL J0630.9−2406 (z > ∼1.239), and 3FGL J0811.2−7529 (z=0.774), detected by Fermi with relatively flat GeV spectra. By observing simultaneously in the near-IR to hard X-ray band, we can well characterize the high end of the synchrotron component of the SED. Thus, fitting the SEDs to synchro-Compton models of the dominant emission from the relativistic jet, we can constrain the underlying particle properties and predict the shape of the GeV Compton component. Standard extragalactic background light (EBL) models explain the high-energy absorption well, with poorer fits for high UV models. The fits show clear evidence for EBL absorption in the Fermi spectrum of our highest redshift source 3FGL J0630.9−2406. While synchrotron self-Compton models adequately describe the SEDs, the situation may be complicated by possible external Compton components. For 3FGL J0811.2−7529, we also discover a nearby serendipitous source in the X-ray data, which is almost certainly another lower synchrotron peak frequency (ν pk) BL Lac, that may contribute flux in the Fermi band. Since our sources are unusual high-luminosity, moderate ν pk BL Lacs we compare these quantities and the Compton dominance, the ratio of peak inverse-Compton to peak synchrotron luminosities (L pk/L sy pk), with those of the full Fermi BL Lac population. Subject headings: BL Lacertae objects: general — BL Lacertae objects: individual (3FGL J0022.1−1855, 3FGL J0630.9−2406, 3FGL J0811.2−7529) — radiation mechanism: non-thermal — galaxies: active 1 Deutsches Elektronen Synchrotron DESY, D-12738 Zeuthen, Germany 2 Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978, USA 3 W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA 4 email: [email protected] 5 Università di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa I-56127 Pisa, Italy 6 Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste, Italy 7 Dipartimento di Fisica, Università di Trieste, I-34127 Trieste, Italy 8 Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy 9 Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, I-35131 Padova, Italy 10 Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy 11 Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari, Italy 12 Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino, Italy 13 Dipartimento di Fisica Generale “Amadeo Avogadro” , Università degli Studi di Torino, I-10125 Torino, Italy 14 Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, Montpellier, France 15 Department of Physics, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa 16 Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, Palaiseau, France 17 Consorzio Interuniversitario per la Fisica Spaziale (CIFS), I-10133 Torino, Italy 18 Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, Italy 19 INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, I-20133 Milano, Italy 20 Agenzia Spaziale Italiana (ASI) Science Data Center, I-00133 Roma, Italy 21 Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia, Italy 22 Dipartimento di Fisica, Università degli Studi di Perugia, I-06123 Perugia, Italy 23 College of Science, George Mason University, Fairfax, VA 22030, resident at Naval Research Laboratory, Washington, DC 20375, USA 24 INAF Osservatorio Astronomico di Roma, I-00040 Monte